There is a known printed circuit board which includes a base film and a conductive pattern disposed on one surface of the base film. Such a printed circuit board is fabricated, for example, by forming a seed layer with a thickness of 1 μm or less by a sputtering method on one surface of a base film, forming a metal plating layer by electroplating on one surface of the seed layer to obtain a metal layer, and etching the metal layer into a desired pattern (refer to Japanese Unexamined Patent Application Publication No. 9-136378).
Usually after formation of circuits, the printed circuit board is inspected to determine the presence or absence of circuit defects with an automated optical inspection system, and is then shipped as a product. Furthermore, in the inspection with the automated optical inspection system, the printed circuit board is irradiated with light, and the presence or absence of circuit defects is determined on the basis of the contrast of reflected light.